CO2 Recovery in Beer Production

During the fermentation process, the yeast feeds on the wort which results in the production of carbon dioxide (CO2 ) and alcohol.

It is best practice to recover the CO2 generated during beer production from the tops of the fermentation tanks/vessels, the maturation vessels and the bright beer tanks. CO2 can then be scrubbed, purified and compressed for storage. It can later be used in-house in a number of brewery operations, e.g. carbonation and bottling, as well as sold or provided for other applications, in the framework of industrial symbiosis.

More in details, the CO2 generated during the fermentation process contains impurities, hydrogen sulphide, oxygen and dimethyl sulphide. These compounds must be removed due to their negative effect on the taste, odour and shelf life of the final products/beer.

The next step after the collection of CO2 is therefore its cleaning. A number of processes can be put in place, e.g. liquefaction and then vaporisation. This means that a high amount of energy is needed for this operation.

A brief outline of a CO2 recovery system would include the following processes:

Foam trap (separator): removes the foam carry-over occasional generated from fermentation

CO2 booster compressor: maintains the fermenter pressure and provides positive pressure for purification and compression

CO2 scrubber: provides bulk removal of water-soluble impurities in an efficient manner using potable water as the scrubbing medium.

CO2 compressor: elevates the gas pressure to allow for efficient purification, dehydration and liquefaction

CO2 aftercooler/precooler: reduces the temperature of the gas, condenses the gaseous CO2 and remove the humidity in the gas

CO2 dryer: removes impurities and water vapour

CO2 liquefaction: conversion of CO2 gas to a liquid form by use of refrigeration

Liquid CO2 tank (storage tank): stores the liquid CO2.

During beer fermentation, about 4 kg CO2 are produced per hecytolitre of beer. Of these 4 kg, about 2 kg can be recovered thanks to currently available CO2 recovery systems. Usually, a brewery requires about 2 kg/hl of CO2 which means that almost the whole CO2 demand can be covered by CO2 recovery.

Environmental benefits

Implementing this technique reduces the amount of CO2 purchased, decreasing the environmental footprint of the final product. This is because industrial production of CO2 to be added into drinks requires a high energy input.

Side effects

Implementing this process requires energy (heat and electricity) and the installation of additional equipment, increasing the environmental footprint of the process.

Applicability

Virtually all breweries use CO2 in some form in their processes, typically for purging and bottling. If not recovered from the brewing process itself beverage-grade or at least food-grade CO2 has to be sourced externally at a cost. The technique is therefore of potential interest to all brewers.

In theory, the technique can be sized to adapt to all scales of beer production. In practice however, micro-scale breweries might find it unattractive to recover their own CO2

The reusable CO2 has to meet certain standards to be reused in the final product, most importantly in terms of residual oxygen concentration, as oxygen in the final products reduces the product shelf life and harms its organoleptic qualities. Therefore the CO2 purity must be checked before its use in final products; to achieve this, the necessary inlet purity for the CO2 treatment is approximately from 95 % to 99.7%. This reduces the scope of potentially recoverable CO2 to only about 50 % of the released CO2 from fermentation. In fact, it is difficult to separate the initial high concentrations of N2 and O2 from the CO2 (CO2 recovery normally begins 24 hours after the start of fermentation to ensure that the incoming fermentation gas has a minimum CO2 concentration of 99.5 % vol).

Economics

CO2 is required at the end of the manufacturing process in order to achieve the fizzy effect in the final product. Therefore on-site generation, by recovering it, reduces the operational costs of the breweries.